WHO has been studying cancer-causing agents for 45 years, and its list numbers in the hundreds.

The group of 120 agents that have shown the greatest risk of causing cancer includes ethanol from alcoholic drinks, coal, hormonal contraceptives and tobacco.

The next group, which has 75 agents, shows "limited evidence of carcinogenicity in humans, sufficient evidence of carcinogenicity in experimental animals," according to the Washington Post. Red meat falls in this group.